1. Field of the Invention
The invention relates to online monitoring of combustion turbines for defects. More specifically, the invention is an apparatus and method for using acoustic signals to monitor the condition of combustion turbine component online.
2. Background Information
Combustion turbines typically operate at extremely high temperatures, for example, 2500xc2x0 F. to 2900xc2x0 F. (1371xc2x0 C. to 1593xc2x0 C.). Such high temperatures will cause failure of various components unless they are protected from the heat. These components include the rotating blades of the turbine, and the vanes for directing gas flow within the turbine. A typical combustion turbine will have three to four rows each of blades and vanes, with approximately 50 to 100 blades or vanes per row, and will typically have approximately 500 total blades and vanes to protect. A commonly used material for vanes and blades is nickel-cobalt. These components are usually insulated by a thermal barrier coating to enable their use within high temperature environments. A typical thermal barrier coating is yttria-zirconia.
Currently, it is necessary to periodically stop the turbine and inspect the components for deterioration of the thermal barrier coating, defects in other coatings, or other defects, for example, formation of cracks. It would be desirable to monitor the condition of these components while the turbine is in use. Avoiding the need to periodically stop the turbine for inspection reduces downtime, increasing the turbine""s efficiency. Similarly, early detection of defects reduces repair costs and outage time, again increasing turbine efficiency. A need exists for providing earlier detection of defects, and a means of locating the defect, simplifying the inspection and repair procedure once a defect is identified.
One proposed system for detecting and locating defects within turbine components is described in U.S. Pat. No. 5,445,027 issued to W. Zxc3x6rner on Aug. 29, 1995. The system involves using a probe on the housing of the turbine to measure the acoustic spectrum of the turbine. This acoustic spectrum is then compared with a reference spectrum, with deviations from this reference spectrum indicating a damaged turbine blade. A preferred embodiment of this method includes generating an acoustic signal to increase the intensity of the acoustic spectrum within the turbine.
U.S. Pat. No. 5,942,690 issued to A. Shvetsky on Aug. 24, 1999, describes an apparatus and method for ultrasonic inspection of rotating machinery while the machinery is in operation. The method uses an ultrasonic transducer to radiate pulses of ultrasonic energy at a frequency substantially equal to a subharmonic of the frequency of the turbine rotation. The transducer will sense reflections of the ultrasonic pulses from the blade, and convert the reflections into an electrical signal. Changes in the reflected signal can indicate a damaged blade. If this apparatus and method were used with a combustion turbine, it would be difficult to precisely direct an acoustic wave through the high pressure, flowing gas present within the turbine.
Accordingly, there is a need to provide an online monitor for identifying the onset of a change in the condition of combustion turbine components. Additionally, there is a need identify the general location of the defect. Further, there is a need to detect the inception of defects within a coating protecting these components.
The invention is a system for monitoring the condition of a component within a combustion turbine during operation of the turbine, and in its preferred form can be used to monitor the thermal barrier coating on the blades and vanes within the turbine. The system relies on detecting changes in the magnitude and/or velocity of acoustic waves created by gas pressure exerted on the vanes (for directing gas flow) and blades (for converting the gas pressure into work).
As the combustion turbine is operated, a pulse signal generator will generate a signal to an acoustic transmitter, which will convert the electrical signal to an acoustic wave for transmittal through a high frequency acoustic waveguide to each vane. Acoustic waves passing through each vane are received by a second acoustic waveguide. An acoustic waveguide receiver will transmit a signal corresponding to the acoustic waves received to an acoustic receiver for conversion of the acoustic signal to an electrical signal. The signal is then transmitted to a filter to remove the lower frequency signals of the turbine from the higher frequency signals to be analyzed. The signal is finally sent to a storage scope and/or computer, permitting the variations in the acoustic waves to be analyzed.
If only monitoring the condition of the vanes, a pulsed acoustic signal may be sent through the vanes. The resulting acoustic wave will have a certain magnitude and velocity when passing through a vane with an intact coating. The magnitude and velocity of the acoustic wave will vary according to the condition and bond strength of the thermal barrier coating, and the strain to which the vane is subjected. As the coating on the vane deteriorates, the magnitude and/or velocity of the resulting acoustic wave will change, indicating that a vane needs servicing.
A rapid sequence of pulses, approximating a steady acoustic wave, or a continuous sine wave, may be generated to measure coating wear on both the blades and the vanes. A rapid sequence of pulses ensures that a pulse is present as a blade passes the vane. The measured magnitude of the acoustic waves at one vane will increase as a blade passes that vane due to the gas pressure, which will produce a regular pattern of increasing and decreasing magnitude in the acoustic waves as long as all blades are in good condition. As before, the magnitude and velocity of the acoustic wave will vary according to the condition and bond strength of the thermal barrier coating, and the strain to which the blade is subjected. As the coating on the blades deteriorates, the magnitude and/or velocity of the resulting acoustic wave will change, indicating that a blade needs servicing.
Alternatively, acoustic signals within the turbine can be monitored without the need for generating the acoustic signal. As each blade passes a vane, the blade will produce a gas pressure pulse and resulting acoustic wave at that vane. The acoustic waves are received by an acoustic waveguide. The acoustic waveguide will transmit the acoustic wave to an acoustic receiver for converting the acoustic signal to an electrical signal. The electrical signal will then be transmitted to a filter to remove the lower frequency signals of the turbine from the higher frequency signals to be analyzed. The signal is finally sent to a storage scope and computer, permitting the variations in the acoustic waves to be analyzed. A particular acoustic signal having increasing magnitude indicates a blade having a deteriorating coating.
It is therefore an aspect of the present invention to provide an apparatus for monitoring the condition of a component within a turbine while the turbine is operating.
It is another aspect of the present invention to provide an apparatus for monitoring the condition of a coating on a component within a turbine while the turbine is operating.
It is therefore a further aspect of the present invention to provide an apparatus for monitoring the condition of a thermal barrier coating on the components of a combustion turbine while the turbine is operating.
It is another aspect of the present invention to provide a method for monitoring the condition of a thermal barrier coating on the components of a combustion turbine while the turbine is operating.
It is a further aspect of the present invention to determine the status of a thermal barrier coating by passing an acoustic wave through that coating, and analyzing the acoustic wave for changes in magnitude.
A better understanding of the present invention can be obtained from the following description, with reference to the drawings.